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When you have two processes and you want to compare the results of them, is it:

(original process)/(new process) or (new process)/(old process)?

There isn't a particular context for this question, but it could apply to compression ratios etc.

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It depends. ${}$ –  J. M. Sep 15 '11 at 15:51
If you had $100$ dollars and now you have $163$, then you have increased your balance by a factor $163/100 = 1.63$, or you have made $(163 - 100)/100 \cdot 100\% = 63\%$ profit. So usually I'd say divide the new by the old. –  TMM Sep 15 '11 at 15:54
I think new/old is common, since it easily allows you to compute things like: "what is the percentage increase/decrease in output this year?". I cannot immediately think of a context where old/new makes more sense. –  Srivatsan Sep 15 '11 at 15:55

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